In a common desktop stapler a striker is linked directly to a handle so that pressing the handle ejects a staple out and through a stack of papers. Three distinct forces must be overcome: breaking off the staple from the rack of staples, piercing the papers, and folding the staple legs behind the papers. As the staple moves through the cycle there are force peaks and force lows. The result is a jerky experience as the user forces the handle down. The handle resists, suddenly gives way, and then resists again. Even though the peak forces are for short durations, they define the difficulty of using a stapler. Empirical information suggests that a conventional stapler requires peak forces of 15 to 30 pounds, depending on the number of paper sheets to be fastened.
It is desirable to limit the peak force required. An effective way to do this is to accumulate the total energy needed to install the staple and then release that energy all at once by striking the staple in an impact blow. This is a type of action commonly used in staple gun tackers. A handle is pressed through a range of motion causing a spring to store energy. The stored energy is suddenly released at a predetermined handle position. A striker linked to the spring ejects and installs a staple released at a predetermined handle position. A striker linked to the spring ejects and installs a staple.
An important advantage of using stored energy to install a staple is that the handle end need not be directly linked to the striker. In a common direct acting desktop stapler the handle front end moves exactly as the staple moves. This means that, for example, 15 lbs. to force a striker, thus a staple, to move 1 mm requires 15 lbs. to move the handle that same 1 mm. If the driving energy is stored, then the handle can be de-linked from the striker. The handle can move more than the striker moves to provide enhanced leverage. For example, the handle, where it is pressed near its front end, may move downward one inch as the spring is deflected, while the striker moves just ½ inch when the spring is released. According to the preceding discussion, force in stapling can be reduced through two ways. First, spring stored energy allows removal of force peaks by averaging forces over a full handle motion. Second, the energy can be stored through a leveraged system.
A stapler must have a method for adding staples to a staple track. In a common direct acting stapler the striker has a rest position immediately above the staple to be ejected. The track may move outward from the front of the stapler to expose a staple loading area since the striker does not obstruct such motion. Or the handle may be linked to a staple pusher whereby pivoting the handle away from the track causes the pusher to retract while the track becomes exposed.
In a practical spring actuated stapler these two common loading systems are not easily provided. The striker rests in its down position just in front of the staple rack. It is not possible to slide the track out past the obstruction created by the striker. Further, since there is an energy storage mechanism linking the striker to the handle in the spring-actuated stapler, it would require a complex design to provide for exposing the staple track by pulling the handle away from the track. An alternate staple loading design is needed.
Among the prior art is UK Patent GB2229129. A spring actuated heavy-duty desktop stapler includes a two piece molded housing with a double torsion (two coil) power spring. A lever has a “U” channel section, and engages an extended handle by means of a roller linkage.
German Patent DT2856-621 shows a staple gun that uses a similar mechanism to the above '129 reference, but as a staple gun tacker, without a base or a forward handle linked to the lever.
U.S. Pat. No. 4,463,890 discloses a standard style desktop stapler with a spring-actuated driver. The striker has a raised rest position, above the staples as in typical direct action staplers. Base 10 overhangs rubber footpads under the base at the distal front and rear ends of base 10.
U.S. Pat. No. 2,271,479 shows a stapler with footpads slightly more closely integrated with the base. The front footpad angles upward and forward to meet the lower edge of the base, leaving a notch under the base.
UK Patent GB2032327 shows re-set spring 12 attached to lever 3 rearward of lever pivot 4.
U.S. Pat. Nos. 5,988,478 and 6,145,728, to the present inventor, show forward action staple guns. In both references the lever has a “U” channel section that partially surrounds the power spring from above. In '728 lever 60 engages striker 80 by two opposed openings 83. Power spring 70 fits into striker opening 87 between the opposed lever openings. In '478, the handle is pivoted to the body by arcuate extensions 32 surrounding post 12.
U.S. Design Pat. Nos. 186,342, B396,377, D413,239, and D437,754, show various base designs. A short center portion of the base is actually or visually raised in these designs.
U.S. Pat. No. 5,699,949 to the present inventor shows a further forward action staple gun. A staple track is at the bottom of the device, behind the numeral 50 in FIG. 1, formed as an upright “U” metal channel. A staple track guiding tab of: the track is seen just to the left and above the numeral 5 in FIG. 1. An opening is seen in the side of the track from which the tab has been formed. A pusher spring resembling a cross hatch shows through this opening in FIG. 1. The tab is made from a cut out portion of the side of the “U” channel.
U.S. Pat. No. 2,218,794 shows a spacer spring 39 that serves a function to releasably limit upward motion of the body through a snap fit. Elongated “ears or bearings 11” position the body laterally above the base in a conventional way by contact between the body sides and the elongated bearings 11. Spring 39 includes various out-of-plane bends to allow it to change length as the body closes against the base. It is therefore not stiff in the lateral direction. Further, rivet 38 does not provide substantial lateral stiffness to spring 39.
U.S. Pat. No. 4,546,909 shows a stapler with a spacer spring a3 or a4 formed as a “punched out” element.
U.S. Pat. No. 4,795,073 shows a spacer spring 19 that is apparently molded as part of the base.
U.S. Pat. No. 4,811,884 shows a base with a rearward attachment to the body. Groove 107 engages tab 108 to hold the base in the fully open position, col. 9, lines 5-13.